User-Agent: Microsoft-Entourage/11.3.3.061214
Date: Fri, 01 Jun 2007 12:54:44 -0700
Subject: Re: Autodetect of software RAID1+0 fails
From: "Luke Lonergan" <llonergan@greenplum.com>
To: "Dimitri" <dimitrik.fr@gmail.com>,
	"Craig James" <craig_james@emolecules.com>
cc: pgsql-performance@postgresql.org
Message-ID: <C285C794.3219A%llonergan@greenplum.com>
Thread-Topic: [PERFORM] Autodetect of software RAID1+0 fails
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In-Reply-To: <5482c80a0706011151y3851c68je5829a2291282b73@mail.gmail.com>
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Dimitri,

LVM is great, one thing to watch out for: it is very slow compared to pure
md.  That will only matter in practice if you want to exceed 1GB/s of
sequential I/O bandwidth.

- Luke


On 6/1/07 11:51 AM, "Dimitri" <dimitrik.fr@gmail.com> wrote:

> Craig,
> 
> to make things working properly here you need to create a config file
> keeping both raid1 and raid0 information (/etc/mdadm/mdadm.conf).
> However if your root filesystem is corrupted, or you loose this file,
> or move disks somewhere else - you are back to the same initial issue
> :))
> 
> So, the solution I've found 100% working in any case is: use mdadm to
> create raid1 devices (as you do already) and then use LVM to create
> raid0 volume on it - LVM writes its own labels on every MD devices and
> will find its volumes peaces automatically! Tested for crash several
> times and was surprised by its robustness :))
> 
> Rgds,
> -Dimitri
> 
> On 6/1/07, Craig James <craig_james@emolecules.com> wrote:
>> Apologies for a somewhat off-topic question, but...
>> 
>> The Linux kernel doesn't properly detect my software RAID1+0 when I boot up.
>>  It detects the two RAID1 arrays, the partitions of which are marked
>> properly.  But it can't find the RAID0 on top of that, because there's no
>> corresponding device to auto-detect.  The result is that it creates /dev/md0
>> and /dev/md1 and assembles the RAID1 devices on bootup, but /dev/md2 isn't
>> created, so the RAID0 can't be assembled at boot time.
>> 
>> Here's what it looks like:
>> 
>> $ cat /proc/mdstat
>> Personalities : [raid0] [raid1]
>> md2 : active raid0 md0[0] md1[1]
>>       234436224 blocks 64k chunks
>> 
>> md1 : active raid1 sde1[1] sdc1[2]
>>       117218176 blocks [2/2] [UU]
>> 
>> md0 : active raid1 sdd1[1] sdb1[0]
>>       117218176 blocks [2/2] [UU]
>> 
>> $ uname -r
>> 2.6.12-1.1381_FC3
>> 
>> After a reboot, I always have to do this:
>> 
>>       mknod /dev/md2 b 9 2
>>       mdadm --assemble /dev/md2 /dev/md0 /dev/md1
>>       mount /dev/md2
>> 
>> What am I missing here?
>> 
>> Thanks,
>> Craig
>> 
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